Messages in this thread | | | Date | Thu, 10 Oct 2013 16:05:37 +0800 | From | Gu Zheng <> | Subject | Re: [RFC/query] kvm async_pf anon pined pages migration |
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On 10/10/2013 04:01 PM, Gleb Natapov wrote:
> On Thu, Oct 10, 2013 at 03:53:08PM +0800, Gu Zheng wrote: >> Hi Gleb, >> >> On 10/10/2013 03:15 PM, Gleb Natapov wrote: >> >>> On Thu, Oct 10, 2013 at 03:05:58PM +0800, chai wen wrote: >>>> On 10/08/2013 03:39 PM, Gleb Natapov wrote: >>>>> On Tue, Oct 08, 2013 at 02:58:22PM +0800, chai wen wrote: >>>>>> On 10/02/2013 12:04 AM, chaiwen wrote: >>>>>>> On 09/30/2013 08:51 PM, Gleb Natapov wrote: >>>>>>>> On Mon, Sep 30, 2013 at 06:03:07PM +0800, chai wen wrote: >>>>>>>>> Hi all >>>>>>>>> >>>>>>>>> Async page fault in kvm currently pin user pages via get_user_pages. >>>>>>>>> when doing page migration,the method can be found via >>>>>>>>> page->mmapping->a_ops->migratepage to offline old pages and migrate to >>>>>>>>> new pages. As to anonymous page there is no file mapping but a anon_vma.So >>>>>>>>> the migration will fall back to some *default* migration method.Anon pages >>>>>>>>> that have been pined in memory by some reasons could be failed in the migration >>>>>>>>> processing because of some reasons like ref-count checking. >>>>>>>>> (or I misunderstand some thing?) >>>>>>>>> >>>>>>>>> Now we want to make these anon pages in async_pf can be migrated, I try some >>>>>>>>> ways.But there are still many problems. The following is one that replaceing >>>>>>>>> the mapping of anon page arbitrarily and doing some thing based on it. >>>>>>>>> Kvm-based virtual machine can works on this patch,but have no experience of >>>>>>>>> offline pages because of the limitaion of resouces.I'll check it later. >>>>>>>>> >>>>>>>>> I don't know weather it is a right direction of this issue. >>>>>>>>> All comments/criticize are welcomed. >>>>>>>> The pinning is not mandatory and can (and probably should) be dropped, but >>>>>>>> pinning that is done by async page faults is short lived. What problems >>>>>>>> are you seeing that warrant the complexity of handling their migration? >>>>>> Hi Gleb >>>>>> >>>>>> As to this issue, I still have some thing not very clear. >>>>>> If pages pinning is successfully holding (although not mandatory) by >>>>>> async page fault. >>>>>> And at the same time page migration happens because of memory >>>>>> hot-remove action. >>>>>> It has 120*hz timeout setting in common page offline processing, >>>>>> could it fail with >>>>>> these async_pf pined pages migration ? >>>>>> What's your opinion about this ? If it may fail under this >>>>>> circumstance, should we do >>>>>> some thing on it ? >>>>>> >>>>> 120 seconds is more than enough time for pinning to go away, but as I >>>>> said the pinning is not even necessary. Patch to remove it is welcomed. >>>> Thank you for your clarification ! I've got it. we will still work on it. >>>> >>> Should be extremely easy. Drop FOLL_GET from GUP in async_pf_execute(). >> >> One lower question, why pinning page is not necessary here? >> > The purpose of GUP here is to bring page from swap, the page itself is > never used directly by async pf code. The page is used when guest > accesses it next time, but that code path does its own GUP.
Got it, thanks for your explanation.:)
Regards, Gu
> > -- > Gleb. >
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